Discharge lamp and electrode



1954 E. ca. F. ARNOTT 2,692,350

DISCHARGE LAMP AND ELECTRODE Filed Jan. 15, 1948 Pas/77V: 6040M p20) 5 C/ifflflUE INVENTOR E a EGuFTfiE/VOTT.

ATTORNEY Patented Oct. 19, 1954 DISCHARGE LAMP AND ELECTRODE Edward G. F. Arnott, Upper Montclair, N. J assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 15, 1948, Serial No. 2,405

14 Claims. 1

This invention relates to gaseous electric discharge devices and, more particularly, to electrodes and auxiliary electrodes therefor.

The principal object of my invention, generally considered, is to increase the efiiciency of such discharge devices by minimizing the loss of potential at the anode.

Another object of my invention is to produce a gaseous electric discharge device having electron-emitting cathodes at opposite ends thereof, and auxiliary electrodes associated therewith to function as anodes and presenting areas large enough to avoid positive anode drop, as well as the formation of oscillations due to insufiicient areas.

A further object of my invention is to increase the efficiency of gaseous electric discharge lamp operation by avoiding unnecessary loss at the electrodes by using auxiliary anode members of relatively large area connected to said electrodes, and formed of desirable material, in which the product of the current density and the anode area is greater than that of the discharge current, and arranged so as to avoid, to as great an extent as possible, restricting the discharge from the cathodes.

Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to the scale drawing:

Figure l is a fragmentary elevational View, with parts in axial section, of a discharge lamp embodying my invention.

Figure 2 is a perspective view of one of the electrodes of the lam-p of Figure 1.

Figure 3 is a view corresponding to Figure 2,

but showing a modification.

Figures 4, 5, and 6 are views also corresponding to Figure 2, but showing other modifications.

Figure 7 is a, fragmentary axial sectional view corresponding to Figure l, but showing a modifica-tion.

Figure 8 is a transverse sectional view, on the line VIII-VIII of Figure 7, in the direction of the arrows.

Figure 9 is a fragmentary axial sectional view corresponding to Figure l, but showing an additional embodiment of my invention.

Figure 10 is a view corresponding to Figure 9, but showing a further embodiment of the invention.

Figure 11 is a diagram to illustrate how my invention increases the efiiciency of operation of discharge lamps.

Discharge lamps of the prior art ordinarily employ small electrodes which on alternating current operation function alternately as anode and cathode. In some instances, said electrodes are provided with extensions or horns which slightly increase the total area of the electrodes and function as anodes.

In a gaseous electric discharge device, such as a fluorescent or other low-pressure ionizable gas discharge tube or. lamp, there will be a positive drop of potential in'the region near the anode, if the anode area is less than some critical value.

Figure 11 shows the three main regions of the discharge; the part a representing the cathode drop region in which a potential loss of from 10 to several hundred volts may exist; the part 1) representing the positive column drop which depends on the length of the discharge and the voltage gradient in the column, which may vary from a few tenths of a volt per centimeter, up to several volts or tens of volts per centimeter; and the part 0 representing the anode loss or drop which may be from a positive value equal to or perhaps somewhat greater than the ionization potential of the gas in the enclosing envelope to a negative value of a few volts.

The operating current which flows in the external circuit to the lamp is determined by the applied voltage, the load impedance, and the total voltage drop across the lamp. In the positive column of the discharge this current, assumed to be normal or in accordance with the lamp rating, is carried mainly by electrons moving from the cathode to the anode with a certain drift velocity. The values of the electron concentration and the drift velocity will adjust themselves so that the current i is distributed over each cross-section of the tube between the electrodes.

At the surface of the anode, however, other conditions exist. The anode receives current depending on the random current density of the discharge determined by the operating current, reference being had to the Langmuir Theory of probes. The random current density a' in the positive column near an anode will be in accord ance with the equation:

where k is Boltzmanns constant, Te the electron temperature, m the mass of an electron, e the electronic charge and n the electron concentration.

The condition for no positive anode drop, where a. is the anode area, is that:

jai'i If a is not large enough for this relation to hold, then not enough electrons will reach the anode to give the required current i, and a positive anode drop will be formed to draw more electrons to the anode. If the anode is made smaller, this positive drop will increase until it reaches a value equalto theionization potential of the gas. When this occurs, ions will be formed near the anode efiectively increasing its area, and the anode drop will cease to increase. In some cases, if a sufiicient number of ions is produced, the anode drop will actually decrease and oscillations may appear. This is a normal condition in lamps of the prior art.

By experimental tests, I have shown that'in a fluorescent lamp discharge, the voltage drop can be reduced by approximately 3 volts by the use of an auxiliary anode having suificient area, as represented by the change from the dotted upper portion of the graph of Figure 11 to the corresponding full line portion. This should result in an increase in efficiency of over 10% in a 20 watt lamp and over in a 40 watt lamp, operating at normal or rated potential with standard ballast. Actual tests showed an increase of in efficiency with such auxiliary anodes used.

Now referring to the embodiment of my invention illustrated in Figures 1 and 2, there is shown a discharge lamp I 1 comprising an elongated hollow cylindrical translucent vitreous or glass envelope IZ containing a rare or inert gaseous filling at low pressure, admixed with mercury vapor, in each end of which is sealed a mount l3 comprising afilamentary cathode I4 coiled around an axis extending diametrically of said envelope and supported by leads I5 and I6 sealed through the press ll of the mount.

In the present embodiment, one of the leads such as It is extended longitudinally of the envelope, as indicated at l8, and a hollow cylindrical metal member I9 is supported thereon generally coaxial with the envelope to function as an auxiliary anode. The hollow cylindrical member 19 is desirably positioned so that the filamentary cathode |4 lies in approximatelyv the plane of its outer edge, but is disposed between its ends and thereby enclosed or surrounded by said member [9 so that said auxiliary anode is disposed between said cathode and the electrode at the other end of the envelope. This form is best applicable for use with a unipotentia-l cathode, or one where the difference in polarity of the ends of the cathode due to alternating current operation is so small that it exerts no deleterious effect.

A lamp was made having anodes as shown in Figure 2 made of nickel sheet, 5 mils in thickness in the form of a cylinder diameter and long/ The anodes were mounted on separate With anodes connected directly to power lines mi Voltage, 49 56. Efficiency, 39.9 L/W H} 36.1 L/W.

When a coiled or.non= unipotential filament is used as a cathode, a construction such as shown in Figure 3 is more desirable, since in this case, it, is immaterial which leg or lead of the filament is connected directly to the circuit fo deficient use. In this case, each one of the two approximately semi-cylindrical anode members 2| and 22 has a surface area suflicient to make the above condition regarding current density and circuit current hold. The form of Figures '1 and 2 and that of Figure 3 are suitable if it is immaterial whether or not the light generated near the oathode is transmitted to the surface of the envelope of the device.

Figure 4 represents a construction like that of Figure 2, except that the auxiliary hollow cylindrical anode portion l9 is formed from screen material rather than from an imperforate plate. Such a construction allows substantially all the light generated within the tube to fall on the tube wall, such as is desired in the case of a fluorescent lamp.

Figure 5 illustrates a construction in which the auxiliary anodes Zl and 22 are generally like the anodes 2i and 22 of Figure 3 but formed from screen material like that of Figure 4.

Figure 6 shows a construction like that of Fig.- ure 5, except that the cathode coil I4 is disposed centrally in a space between the auxiliary screen anodes 2N and 22 rather than approximately in the plane of the outer endsof said auxiliary anodes.

Figures 7 and 8 illustrate a construction using anode plates la radially disposed in order to accomplish the results obtained by the forms of Figures 4, 5, and 6 without using foraminous or screen material. In these figures there is shown a fragmentary portion of a discharge lamp ll comprising an elongated hollow cylindrical translucent vitreous or glass envelope [2 containing a filling like that of the preceding embodiments, in each end of which is sealed a mount [3P comprising a filamentary cathode M supported by leads [5 and Mi sealed through the press I! of said mount.

In. the present embodiment, onev of the leads V such as I (i is beyond its connection with the cathode M bent and extended radially toward the axis of the envelope for a short distance and then bent parallel to the axis and extended away from the press I'l as indicated at |8 The extension l8 carries a pair of anode rings 29 and 3|, which in turn support the radial anode plates [9 presenting an area aggregating that of the otherembodiments and'not appreciably interfering with the transmission of radiations to the enclosing envelope.

As previously stated, the: purpose of such an anode construction is to reduce the normallypresent positive anode drop, and thereby decrease the overall discharge drop and hence the operating efilciency. The elficiency may be further increased by making the anodes of material of higher than usual work functions, such as platinum, tungsten, or molybdenum, reference being made to Table I, page 17, The Physics of Electron Tubes, by L. R. Koller, McGraw-Hill, 1934. To make further use of this advantageous property of increased anode area, the form shown in Figures 9 and 10 are proposed. In Figure 9, the auxiliary, and in this case cup, anode l9 of Kovar, per definition in Lempert et a1. Patent- No. 2,279,831, dated April l4, 19l2-,.or other metal that will properly seal to glass is made; part of the envelope I2 and sealed to the end thereorin such a manner that an exposed inner cylindrical metal surface 13 projects along. the devicetfrom:

the cathode M The cathode M is mounted between a lead l5 extending from the auxiliary cup anode l9 and a lead 6 passing through and insulated from said cup as by means of a glass bead 24.

The discharge device I l is, in this instance, as is contemplated for the previous forms, shown with a base 25 applied to an end and carrying extornal contact pins 26 and 27, respectively connected to the cup anode 19 by a conductor 28 and the lead Hi In this way, the distance between the cathodes is increased without increasing the overall length of the device. This increase in the distance causes an increase in discharge drop which may be approximately equal to the decrease obtained by the use of the large anode surfaces. Thus, a construction is obtained which will operate at the same current and voltage as the devices of the prior art, but will have an increased lighted length and, therefore, increased efficiency.

Figure shows a similar construction in which the cup [9 has an inside surface 23 prepared in such a way as to provide for a good refiection of both visible and ultra-violet radiations. This will increase the efficiency of the device by returning thereinto such radiation as is normally absorbed in the ends of a lamp of the prior art. In the present embodiment, the oathode cup l9 is provided with leads 26 and N which are rigid and sufficiently strong to act as base contact pins, like the members 26 and 27 of the preceding embodiment. The cathode coil l 4 has one end supported on the lead l5 secured to the anode cup W, and the other end secured to the inner end of the pin 2?, which is insulated from said cup as by means of a glass or other insulating bead 24 In this instance, the outer surface of the cup 19 is desirably coated with insulating material to eliminate the hazard of electric shock, as indicated at 32.

From the foregoing, it will be seen that I have devised a lamp which has increased efficiency due to avoiding the loss of potential normally encountered at the anode. In addition to this advantage, removal of the oscillations in the voltage drop removes a potential source of radio interference, since the shape of these oscillations is such as might be expected to generate high frequency effects. By having the auxiliary electrode surround its filament, rather than being displaced toward the opposite end of the envelope and thereby exposing its filament, the reduction in the length of the positive column by said auxiliary electrode is minimized.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

I claim:

1. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low pressure inert gaseous atmosphere therein, each of said electrodes comprising a filament adapted to be heated to electron-emitting temperature, leads to each filament, and an auxiliary approximately semi-cylindrical hollow electrode connected to each of said leads to function as an anode surrounding the adjacent filament presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the 6. positive column, while minimizing the reduction in the length of the positive column.

2. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low pressure inert gaseous atmosphere therein, each of said electrodes comprising a filament adapted to be heated to electron-emitting temperature, leads to each filament, and an auxiliary hollow cylindrical electrode formed of screen material connected to one of said leads to function as an anode surrounding the adjacent filament presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the positive column, while minimizing the reduction in the length of the positive column.

3. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low-pressure inert gaseous atmosphere therein, each of said electrodes comprising an electron-emitting filament, leads to each filament and extended therebeyond, and an auxiliary approximately semicylindrical hollow electrode connected to each of said leads and formed of screen material to function as an anode surrounding the adjacent filament without cutting off much light to the envelope from the discharge, presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the positive column, while minimizing the reduction in the length of the positive column.

4. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low-pressure inert gaseous atmosphere therein, each of said electrodes comprising a filament adapted to be heated to electron-emitting temperature, leads to each filament, and an auxiliary cup-shaped metal electrode formed as a closure at each end of the envelope, connected to only one of said leads to function as an anode and presenting an area large enough to avoid anode drop.

5. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low-pressure inert gaseous atmosphere therein, each of said electrodes comprising a filament adapted to be heated to electron-emitting temperatures, leads to said filament, at least one of said leads being extended beyond said filament, and auxiliary electrode means supported on said lead, said means comprising a plurality of plates extending radially from the axis of the envelope, functioning as an anode, presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the positive col-- umn, while minimizing the reduction in the length of the positive column.

6. An electric discharge device comprising an elongated translucent vitreous envelope, a metal cup sealed to and forming a closure at each end of said envelope and presenting a relatively large internal area, a low pressure ionizable gas filling for said envelope, an electrode supported in said cup and comprising a filament adapted to be heated to electron-emitting temperature, leads to said filament, one of said leads being connected to, and the other passing through and insulated from, said cup, whereby said cup functions as auxiliary anode means and presents an area large enough to avoid anode drop.

'7. An electric discharge device comprisingan elongated translucent vitreous envelope, a low pressure ionizable gas filling for said envelope, a metal cup sealed to and forming a closure at each end of said envelope and presenting a relatively-large internal area prepared for good reflection of both visible and ultra-violet radiation, and electrode supported in each of said cups and comprising a filament adapted to be heated to electron-emitting temperature, leads to each of said filaments, said leads being sufiiciently strong to act as base contact pins, one of the leads for each cup being connected to, the other passing through and insulated from, said cup, whereby each cup functions as auxiliary anode means and insulating material as a coating on the outer surface of each cup to eliminate the hazard of electric shock.

8. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low pressure inert gaseous atmosphere therein, each of said electrodes comprising a filament adapted to be heated to electron-emitting temperature, leads to each filament, and an auxiliary approximately semi-cylindrical electrode connected to each of said leads and positioned so that the adjacent filament is disposed centrally in the space between its pair of semi-cylindrical electrodes, with the auxiliary electrodes functioning as anodes, each presenting an area large enough to'avoid anode drop, and so not smaller than the rated or operating current divided by the random cur rent density in the positive column, while minimizing the reduction in the length of the positive column.

9. In an electric discharge device, an envelope, a filling in said envelope of argon at a pressure of about 3.6 millimeters admixed with mercury vapor, an, electrode comprising a cathode filament adapted to be heated to electron-emitting temperature, leads to said filament, and an auxiliary hollow anode surrounding said filament, connected to one of said leads and presenting an inner area of about 1.77 square inches to avoid anode drop.

10. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, an atmosphere therein of argon at a pressure of about 3.6 millimeters admixed with mercury vapor, at least one of said electrodes comprising a cathode filament, lead means to said filament, and auxiliary hollow anode means surrounding said filament, con nected to said lead means, and presenting an inner area of about 1.77 square inches to effect an increase in efficiency and reduce the necessary operating voltage 11. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low-pressure inert gaseous atmosphere therein, at least one of said electrodes comprising a filamentary cathode portion, lead means to said portion, and hollow auxiliary anode means surrounding said filamentary portion and connected to said lead 8 means, presenting. an area largeenoug-h to avoid anode :drop, and so not smaller than the rated or operating current divided by the random current density in the positive column, while minimizing the reduction in the length of the positive column.

12. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low pressure inert gaseous atmosphere therein, at least one of said electrodes comprising a cathode filament adapted to be heated to electron-emitting temperature, leads to said filament and an auxiliary hollow cylindrical anode surrounding said filament and connected to only one of said leads, presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the positive column, while minimizing the reduction in the length of the positive column.

13. An electric discharge device comprising an elongated translucent vitreous envelope, an electrode sealed in each end thereof, a low-pressure inert gaseous atmosphere therein, at least one of said electrodes comprising a cathode filament adapted to be heated to electron-emitting temperature, leads to said filament sealed through the adjacent portion of said envelope, at least one of said leads being extended beyond said filament, and an auxiliary hollow cylindrical anode surrounding said filament and supported on said extension, presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the positive column, while minimizing the reduction in the length of the positive column.

14. An electric discharge'device comprising an elongated translucent vitreous cylindrical envelope, an electrode sealed in each end thereof, a low-pressure inert gaseous atmosphere therein, each of said electrodes comprising a cathode filament adapted to be heated to electron-emitting temperature, leads to each filament, only one of the leads to each filamentbeing extended beyond its filament, and an auxiliary hollow cylindrical anode, generally coaxial with said envelope, connected to each of said extensions, surrounding the adjacent filament, presenting an area large enough to avoid anode drop, and so not smaller than the rated or operating current divided by the random current density in the positive column while minimizing the reduction in the length of the positive column.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,053,879 Spanner Sept. 8, 1936 2,071,426 Pennybacker Feb. 23, 1937 2,182,732 Meyer Dec. 5, 1939 2,233,741 Kirsten Mar. 4, 1941 2,283,216 Lowry May 19, 1942 2,405,089 Craig July 30, 1946 2,429,118 Besser Oct. 14, 1947 2,433,218 Herzog Dec. 23, 1947 

